1. Field of the Invention
The present invention relates to a lens apparatus, in particular, a lens apparatus for operating a plurality of lens units by a cam ring, which is held by means including a driver capable of operating the lens units in an optical-axis direction within the cam ring, and an image pickup system including the same.
2. Description of the Related Art
A zoom lens system includes a zoom section generally including a magnification-varying lens unit and an aberration correction lens unit. The zoom lens system has a configuration in which the magnification-varying lens unit and the aberration correction lens unit are operated by a cam ring. The magnification-varying lens unit includes a multi-lens group corresponding to a plurality of lens units obtained by division. In particular, broadcast equipment is sometimes operated under conditions in which an operator performs a magnification-varying operation by a driver which is both electrically and manually operated. In each of the case where the driver is electrically operated and the case where the driver is manually operated, high operation followability is required. A structure suitable to satisfy the request of high operation followability is a cam mechanism. The operation followability can be ensured by directly connecting the cam mechanism to an operating unit. In order to operate the magnification-varying lens unit including the plurality of lens units obtained by the division, however, it is necessary to provide as many cam grooves as the number of divisions. For example, Japanese Patent Application Laid-Open No. H11-326734 discloses the following structure for operating a zoom lens system (paragraphs [0006] to [0008], FIGS. 4A and 4B, and the like). Specifically, the magnification-varying lens group is divided into two lens units. One cam groove for operating the thus obtained two magnification-varying lens units is provided to a cam member. The cam groove is configured so that a subject-side sliding surface and an image plane-side sliding surface of the cam groove forms driving loci necessary for varying the magnification of the respective magnification-varying lens units. The magnification-varying lens units are brought into abutment to the corresponding sliding surfaces, respectively. Japanese Patent Application Laid-Open No. H11-109212 discloses a structure in which a correction optical system driven in association with the magnification-varying lens unit is divided so as to enhance the followability of an associated operation with a focus optical system (paragraphs [0004] to [0007], FIGS. 1A and 1B, and the like).
In the related art disclosed in Japanese Patent Application Laid-Open No. H11-326734 and Japanese Patent Application Laid-Open No. H11-109212, the plurality of magnification-varying lens units obtained by the division is driven by the associated operation of a curved cam and a straight cam. In this structure, one cam groove is required for each optical unit as the number of optical units to be moved increases. Therefore, the structure for generating the curved cam is required to ensure a thickness in the optical-axis direction. As a result, a cam ring structure is disadvantageously increased in size. Moreover, for driving, the structure follows only the movement generated by the curved cam. Therefore, for example, in the case where zoom control for driving the magnification-varying lens units is performed so as to cancel an angle-of-field variation caused with the driving of the focus lens unit, controlled driving cannot be performed at a zoom end because an area where the cam groove is movable is not present at the zoom end. In the case of, for example, Japanese Patent Application Laid-Open No. H11-326734, the cam groove is divided into a forward part and a backward part to be respectively used for the magnification-varying lens units obtained by the division so as not to increase the number of cam grooves. Even with the efforts for preventing the number of cam grooves from being increased, a width of the cam groove itself is increased. Therefore, a total length of the cam ring is disadvantageously increased. Accordingly, even though a control operation for correcting the angle-of-field variation based on the focusing the driving control of the zoom unit is desired to be performed, the desired control cannot be performed at the zoom end.
A lens apparatus disclosed in Japanese Patent Application Laid-Open No. H11-109212 has a configuration in which the above-mentioned control can be performed even at the zoom end. When a driving unit is provided inside the optical system, however, a power source for feeding power to the driving unit or communication means for positional detection is exposed inside a lens barrel. Thus, it is presumable that harmful light reflection is caused or external appearance quality deteriorates thereby.
Moreover, in Japanese Patent Application Laid-Open NO. H11-109212, a structure of line connection for driving the driving unit is not described in detail. Therefore, a structure for driving the driving unit provided inside the optical system without affecting optical performance is not described.